This invention relates to electrostatic spray systems, and, more specifically, to hand-held electrostatic spray guns.
Electrostatic spray coating is an established art. In conventional electrostatic spray coating systems, a fluid coating material such as paint, varnish, lacquer and the like is projected toward an object to be coated in an atomized or particulate form from a dispensing device. The object to be coated is held at electrically ground potential and either just before, at, or just after being dispensed from the gun, the coating material is imparted an electrical charge so that it will be electrostatically attracted toward the object to be coated.
In such systems, a typical form of dispensing device is an electrostatic spray gun which is held in hand by an operator who moves the gun to deposit a uniform, smooth coating on the surface of the object. In such hand-held guns, it is highly desirable that the gun be lightweight and compact and that it be evenly balanced so that it may be held by an operator for extended periods of time without tiring the operator. It is also highly desirable that the gun have good transfer efficiency and a high degree of reliability as well as repairability.
That is, in normal operation, the coating material such as paint tends to wear various parts of the gun such as the air valve assembly controlling the flow of atomizing and fan-shaping air through the gun. This is a particular problem in electrostatic spray systems because the paint tends to be attracted to the gun itself thereby getting inside the gun where its abrasive nature can cause wear of valve parts. When valve parts begin to wear, they begin to leak and the gun loses efficiency. Prior art guns because of complicated structure and internal valving were not always easily repairable. Therefore, repair would require removal of the gun from operation for what might be extended periods of time.
Because of the high voltage involved in electrostatic spray coating, certain safety precautions must also be observed in the construction and operation of electrostatic coating devices. For example, when spraying many of the coating materials in use today, including powders, a flammable atmosphere results in the area of coating operation. The high voltage electrostatic charging circuit through the gun causes energy to be capacitively stored in the metallic components of the gun. Thus, if the gun is brought too close to any grounded object, the possibility arises that a spark will jump between the high voltage circuit in the gun and the grounded object igniting the flammable atmosphere in the coating area. The amount of this capacitively stored energy increases as the square of the voltage.